Dynamic Model for an Automotive Overhead Valve-Gear System

Abstract

This research presents a lumped-parameter model, distinct from the ones developed until the present time, easily adaptable for its analog/hybrid simulation, and that combines favorably its simplicity and precision to represent appropriately an automotive valve gear system by means of the inclusion of the hydraulic lifter and of the viscous forces produced by its guide. The checking of this new mathematical model has been accomplished by means of a qualitative comparison with other models previously devised. This model will be useful in the design stage to predict the speed at which the valve jump occurs.

Determination of the Toss Speed for an Automotive Valve-Gear System

“…An appropriate description of the operation of the hydraulic valve lifter and its first detailed modeling appears in [13]. An alternative scheme for a simpler modeling of the hydraulic lifter was devised in [21]. A real automotive hydraulic tappet is considered in this work, and the equivalent parameters have been obtained with reference to the axis of valve motion.…”

“…The viscous damping is modeled by a damper [21,23] of constant c = cr + cs (=32.6 N-s/m), where cs (=7.10 N -s/m, taken from [24]) is the coefficient of viscous damping in the valve spring [23]. Thus, the viscous damping force applied to the valve is expressed as follows (d) Valve Seat.…”

“…Assuming a permanent contact, the polynomial cam activates a hydraulic lifter, whose displacement from the base circle of the cam is measured by coordinate y [21].…”

“…It is assumed that the valve seat behaves as a viscoelastic material lacking mass, capable of supporting only compressive loads [13,21,23,24], and that suffers a deflection d4=F4/k4 (=0.00000084 m) in its static equilibrium position, where the preload F4 (=11 N) has been computed as the difference between the valve-spring load required to separate the valve from its seat (=356 N, as reported in [23] that the static pivot load required to maintain the valve unseated was 980 N) and the valve spring preload (=345 N, reported in [24]). Thus, the valve seat has been represented by a spring of constant k4 (=13100000 N/m, taken from [24]) in parallel with a damper of constant c4 (=903 N-s/m, taken from [24]), according to the Voight model [10,29].…”